YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



201 



In the third growth zone, frequently a very nar- 

 row ring of closely spaced circuli is visible in the 

 midst of the widely spaced ones. This ring is less 

 prominent than the rings of closely spaced, circuli 

 terminating the second and third growth zones. 

 We have considered that this ring is associated 

 with spawning and is not a true growth ring com- 

 parable to the others which we have counted. If 

 it is a spawning mark, it would be expected to 

 appear in subsequent growth zones, but it is not 

 apparent because the widely spaced circuli are 

 so few in growth zones after the third. 



Examination of a series of scale samples taken 

 throughout the year revealed that the new growth 

 ring begins to form from January to March, and 

 that it is apparent earliest in fish with two com- 

 pleted rings and later in the older fish. By the 

 middle of March, almost all scales show the begin- 

 ning of the new growth ring. Since the spawning 

 season commences in late March, we have desig- 

 nated April 1 as beginning another year in the life 

 of the fish, and in counting the growth rings, we 

 have not included those rings completed during 

 January, February, or March. 



The consistent appearance of new growth at 

 one season of the year is evidence that these 

 growth rings are true annuli. Additional evi- 

 dence appears from the facts (which will be de- 

 veloped later in this paper) that the growth rings 

 are added systematically as growth proceeds, that 

 a progression of modes in length-frequency data 

 agrees closely with the length of the fish at corre- 

 sponding ages estimated from the scales, and that 

 there are consistencies in the data on age compo- 

 sition and in the changes in the average length of 

 each age group which would be unlikely if the 

 rings were not annuli. It will also be shown that 

 there is good agreement between the mean lengths 

 of yellowtail aged by scales during this study and 

 those aged by otoliths by Scott (1954). Further- 

 more, the theoretical ultimate length computed 

 from the lengths at each age is very close to the 

 maximum length observed. 



The age determinations used in this paper were 

 made by Raymond J. Buller and Dexter S. Haven 

 during a single period of a few months. The 

 scale impressions were enlarged by a micropro- 

 jector and read independently by each worker. 

 After preliminary trials to establish a uniform 



technique, the two men were able to agree on the 

 reading of more than 90 percent of the scales ex- 

 amined. Due to the scarcity of older scales and 

 the difficulty of reading them, the scales aged 6 

 years and older were combined in one group in 

 the first quarter and ages 7 and older in the other 

 quarters. 



Scales that were not read identically by the two 

 readers were discarded. Since the scales become 

 more difficult to read with increasing age of the 

 fish, discarding them could change the propor- 

 tions of older fish in the samples. Fortunately 

 this did not happen, as indicated in figure 16 

 where the percentage length distributions of the 

 yellowtail whose ages were determined from 

 scales are compared with the percentage length 

 distributions of the fish that were measured. 

 Only very small differences in composition are 

 evident, the greatest difference being a greater 

 percentage of females in the 39- to 43-cm. group 

 of aged fish which was compensated by a smaller 

 percentage in the 35- to 38-cm. group. The pro- 

 portion of males was almost identical — 34.50 per- 

 cent in the aged fish, 34.67 percent in the meas- 

 ured fish. 



-i 1 1 r 



MALES 



• AGES DETERMINED 



TOTAL MEASURED 



20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 

 LENGTH -CENTIMETERS 



Figure 16. — Comparison of the percent length distribu- 

 tions of 7,924 yellowtail whose ages were determined 

 from scales with 37,075 fish that were measured, 1943 

 through 1947. 



